Study On The Method Of Precision Current Control Of Resistance Spot-welder

With the rapid development of science and technology,welding control technology has been widely used.The traditional power frequency resistance spot welder can no longer meet demand in the business.Therefore,the research and design of a low-cost,high-precision and real-time power frequency spot welder has become a necessary trend for development.The paper analyzes the control parameters that affect the welding quality,the welding characteristics of the welding material,and the thyristor conduction characteristics.For the problem of long control cycle time of power frequency resistance spot welder and the problem that the welding current caused by dynamic resistance cannot be adjusted in time,a method of adding feed-forward control based on conventional control is proposed.The specific method is to analyze the dynamic resistance change rule of the welding material in the welding process,introduce the dynamic current data obtained into the calculation of the conduction angle of the next cycle,and correct the conduction angle in advance,as a result,a more accurate welding current can be obtained.This paper designs a unique control algorithm for the characteristics of power frequency spot welder,which has better effect than the conventional control algorithm.This subject selects high-performance,low-power ARM microprocessor STM32F103ZET6 as the core chip of the whole power frequency resistance spot welding machine control system.According to the analysis and selection of the control system scheme,reasonable and reliable hardware circuits and software systems are designed to achieve precise control of welding time and welding current.The hardware circuit design mainly includes power supply circuit,AC zero signal acquisition and processing circuit,thyristor trigger circuit design,detection signal processing circuit and liquid crystal display circuit design.The software design program includes zero pulse signal program,timing triggered interrupt program and A/D conversion complete interrupt program flow.This paper discusses the A/D conversion speed requirements and calculation accuracy of the welding current feedback link,and proposes an effective method that the accuracy of the feedback current calculation is guaranteed by the ordinary microprocessor,and a more effective solution for real-time correction of dynamic current data using feedback information.This topic adopts the modular design idea and designs the program for each module of the system,which makes the control structure more reasonable and more efficient,and realizes the precise control of the spot welder.Finally,the feasibility of this control scheme was verified through a large number of experiment.The resistance spot welder constant current control system designed in this project has the characteristics of high real-time performance,high integration,high control accuracy and good intelligence,and it has certain innovation value,theory and engineering practice value.